Semiconductor nanocrystals (hereinafter “nanocrystals” or “NCs”) are desirable for use in LEEs due to properties such as ease of tunability and high emission quantum yield (hereinafter “QY”). For use in an LEE, the nanocrystals preferably are incorporated into a dense film; however, nanocrystal use in LEE dense films suffers from disadvantages, such as reduced QY. Without being limited by theory, it is thought that, due to a distribution of QYs in a given NC ensemble, close proximity of nanocrystals allows undesirable energy transfer from high QY nanocrystals to any nearby low QY nanocrystals (“bad” energy transfer). Forster energy transfer is the most dominant energy transfer process that occurs between NCs and the rate of this process correlates to r−6, where r is the distance between the centers of the NC's. This process generally results in loss of emission efficiency as well as a shifting of the emission spectrum to longer wavelengths, also known as “red shift.”
Traditionally, solutions to this problem have focused on limiting the transfer of energy between nanocrystals, for example, by diluting the concentration of nanocrystals in the film. However, the presence of fewer nanocrystals leads to a lower probability of excitation, lower emitter density, and thus reduced brightness.
A need exists, therefore, for compositions comprising nanocrystals which do not exhibit reduced brightness and red-shifted emission when used in dense film LEE's.